Can someone explain this how it demonstrates the property ho

Can someone explain this how it demonstrates the property holds. A set of vertices is a vertex cover if and only if its complement is an independent set.

Solution

Vertex cover of the graph A is ( d,c,e,f) . Vertex covering no. is 4. the complement of this set is shown in the figure (d) where all the four of the vertex cover set i.e. (d,c,e,f) set are independent